Maraṇasati is the recollection of death, which the Buddha urged his monks to practise with every breath. Reflecting that life is fragile and death certain rouses urgency, loosens attachment and gives each moment its value. Similar practices are found in Stoicism and Christian monasticism.
Maraṇasati
Mindfulness of death: remembering that death is certain and its time uncertain.
Also: Maranasati, mindfulness of death